Both Penaeus vannamei and P. stylirostris originate on the Western Pacific coast of Latin America from Peru in the south to Mexico in the north.

They were introduced from the early 1970s to the Pacific Islands, where research was conducted into breeding and their potential for aquaculture. During the late 1970s and early 1980s they were introduced to Hawaii and the Eastern Atlantic Coast of the Americas from South Carolina and Texas in the North to Central America and as far south as Brazil.

The culture industry for P. stylirostris in Latin America is largely confined to Mexico, but P. vannamei has become the primary cultured species in the Americas from the USA to Brazil over the past 20-25 years. Total production of this species in the American region probably amounted to some 213 800 metric tonnes, worth US$ 1.1 billion2 in 2002.

P. vannamei was introduced into Asia experimentally from 1978-79, but commercially only since 1996 into Mainland China and Taiwan Province of China, followed by most of the other coastal Asian countries in 2000-01. Experimental introductions of specific pathogen free (SPF) 'supershrimp' P. stylirostris have been made into various Asian countries since 2000, but the only country to develop an industry to date has been Brunei.

Beginning in 1996, P. vannamei was introduced into Asia on a commercial scale. This started in Mainland China and Taiwan Province of China and subsequently spread to the Philippines, Indonesia, Viet Nam, Thailand, Malaysia and India. These introductions, their advantages and disadvantages and potential problems are the focus of this report.

China now has a large and flourishing industry for P. vannamei, with Mainland China producing more than 270 000 metric tonnes in 2002 and an estimated 300000 metric tonnes (71 percent of the country?s total shrimp production) in 2003, which is higher than the current production of the whole of the Americas. Other Asian countries with developing industries for this species include Thailand (120 000 metric tonnes estimated production for 2003), Viet Nam and Indonesia (30000 metric tonnes estimated for 2003 each), with Taiwan Province of China, the Philippines, Malaysia and India together producing several thousand tonnes.

Total production of P. vannamei in Asia was approximately 316000 metric tonnes in 2002, and it has been estimated that this has increased to nearly 500000 metric tonnes in 2003, which is worth approximately US$ 4 billion in terms of export income. However, not all the product is exported and a large local demand exists in some Asian countries.

The main reason behind the importation of P. vannamei to Asia has been the perceived poor performance, slow growth rate and disease susceptibility of the major indigenous cultured shrimp species, P. chinensis in China and P. monodon virtually everywhere else. Shrimp production in Asia has been characterized by serious viral pathogens causing significant losses to the culture industries of most Asian countries over the past decade and slowing down of growth in production.

It was not until the late 1990s, spurred by the production of the imported P. vannamei, that Asian (and therefore world) production levels have begun to rapidly increase again. By comparison, P. vannamei production has greatly reduced in Latin America also as a result of disease problems, however, there has so far been little sign of recovery.

In Asia, first Yellowhead Virus (YHV) from 1992 and later White Spot Syndrome Virus (WSSV) from 1994 caused continuing direct losses of approximately US$ 1 billion per year to the native cultured shrimp industry. In Latin America, first Taura Syndrome Virus (TSV) from 1993 and later, particularly, WSSV from 1999 caused direct losses of approximately US$0.5 billion per year after WSSV. Ancillary losses involving supporting sectors of the industry, jobs, and market and bank confidence put the final loss much higher.

It is widely believed that these three most economically significant viral pathogens (and a host of other pathogens) have been introduced to the Asian and Latin American countries suffering these losses through the careless introduction of live shrimp stocks. Most Asian countries have legislated against the introduction of P. vannamei due to fears over the possibility of introducing new pathogenic viruses and other diseases from Latin America to Asia. Many governments have allowed importation of supposedly disease free stocks that are available for this species from the USA.

The encouraging trial results, the industry-perceived benefits, including superior disease resistance, growth rate and other advantages, allied with problems in controlling the imports from other countries, have led to the widespread introduction of this species to Asia, primarily by commercial farmers. Unfortunately, importation of cheaper, non-disease free stock has resulted in the introduction of serious viral pathogens (particularly TSV) into a number of Asian countries, including Mainland China, Taiwan Province of China, Thailand and Indonesia, and maybe more.

Although TSV is not reported to have affected indigenous cultured or wild shrimp populations, insufficient time and research have been conducted on this issue and there is a need for caution. TSV is a highly mutable virus, capable of mutating into more virulent strains, which are able to infect other species. In addition, other viruses probably imported with P. vannamei, for example a new LOVV-like virus, have been implicated in actually causing the slow growth problems currently being encountered with the culture of the indigenous P. monodon. There remain many unanswered questions regarding the possible effects of introduced species and associated pathogens on other cultured and wild shrimp populations in Asia.

For such reasons there has been caution on the part of many Asian governments. However, this caution has not been demonstrated by the private sector, which has been bringing stocks of illegal and often disease carrying P. vannamei into Asia from many locations, as well as moving infected stocks within Asia. The commercial success of these introductions, despite disease problems, has allowed the development of substantial culture industries for these alien Penaeids within Asia and in China and Thailand in particular. One effect of this is that it is rapidly becoming difficult to control the importation and development of this new industry.

Despite the problems with disease transfer, P. vannamei (and P. stylirostris) does offer a number of advantages over P. monodon for the Asian shrimp farmer.

These are largely associated with the ability to close the life cycle and produce broodstock within the culture ponds. This relieves the necessity of returning to the wild for stocks of broodstock or postlarvae (PL) and permits domestication and genetic selection for favourable traits such as growth rate, disease resistance and rapid maturation. Through these means, domesticated stocks of SPF and specific pathogen resistant (SPR) shrimp have been developed and are currently commercially available from the USA.

Other specific advantages include rapid growth rate, tolerance of high stocking density, tolerance of low salinities and temperatures, lower protein requirements (and therefore production costs), certain disease resistance (if SPR stocks are used), and high survival during larval rearing. However, there are also disadvantages, including their acting as a carrier of various viral pathogens new to Asia, a lack of knowledge of culture techniques (particularly for broodstock development) in Asia, smaller final size and hence lower market price than P. monodon, need for high technology for intensive ponds, competition with Latin America for markets, and a lack of support for farmers due to their often illegal status. Informed decisions regarding these pros and cons need to be taken, with close cooperation between governments, the private sector and NGOs to decide on the best course of action to take. Unfortunately, due to the rapid rise of P. vannamei, there has been little time for such considered actions concerning shrimp imports and movements.

The recent publication of a number of codes of conduct and management guidelines (BMPs) for the transboundary importation of alien shrimp and their subsequent culture by, amongst others, FAO, the OIE, NACA, ASEAN, SEAFDEC and the GAA have clearly defined most of the issues involved. With the availability of SPF and SPF/SPR stocks of P. vannamei and P. stylirostris from the Americas, Asia has had the opportunity to decide whether to responsibly undertake such importations for the betterment of their shrimp culture industries and national economies, whilst avoiding the potential problems with viral diseases and biodiversity issues. However, a number of factors are described to have prevented this ideal situation from manifesting. Although many of the potential problems related to transboundary movements of shrimp and their viral passengers are as yet unknown, it is important that Asian governments take action in legislating control over this industry.

Examples of countries that have managed to legislate for and enforce codes of conduct and management practices (as outlined in this report), and develop successful industries for the culture of imported P. vannamei, include the USA (and especially Hawaii), Venezuela and Brazil. These countries have succeeded despite early failures and disease episodes, demonstrating that such measures can and do work if rigorously applied.

This report has attempted to gather all of the currently available data on the extent of P. vannamei and P. stylirostris importation and culture in Asia, its potential problems and benefits, and in this way serve as a source document from which to investigate further the means by which control over this issue might be re-established.

Recommendations aimed at controlling the importation, testing and culture of these species have been made for all levels and are included in this report.